JPS5867831A - Method for heating steel strip in direct firing type heating furnace - Google Patents

Abstract

PURPOSE:To carry out rapid and accurate heating control, by a method wherein a steel strip is heated to an objective temp. while the air/fuel ratios of all burners in a prior and a posterior stages are maintained in an optimum state and, while the temp. distribution in the width direction of the steel strip directly after passing a heating furnace is detected, the pressure of air or the pressure of a fuel gas to the burner is controlled by every plural blocks in the posterior stage in accordance with the detected value. CONSTITUTION:A ceiling burner group is divided into a prior stage A and a posterior stage B and a steel strip is heated to an objective temp. while the air/fuel ratios of all burners in the prior and the posterior stages are maintained in an optimum state. The temp. of the steel strip directly after passing a heating furnace is detected at positions corresponding to each blocks B1, B2, B3 by thermometers 41, 42, 43. For example, when the measured value by the thermometer 41 becomes lower than the objective value, an air pressure adjusting valve 92 for controlling an air supply amount to the block B1 is adjusted to a direction for increasing the flow amount of air. With this adjustment, the combustion of the burner to the block B1 is intensified by the action of a differential pressure adjusting valve 132. Therefore, the heating temp. of the steel strip is made uniform in the width direction thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heating a steel strip in a direct-fired heating furnace, which is widely applied, for example, to an oxidation furnace in a continuous hot-dip galvanizing line, and more specifically to a method for heating a steel strip in a fired state of a copper strip. The present invention relates to a heating method that prevents variations (hereinafter referred to as uneven baking) as much as possible.

In the oxidation furnace of the Metsuki line mentioned above, when heating the steel strip, the on-site worker controls the amount of fuel supplied to the burner appropriately by operating the burner cock while observing the burnt condition of the copper strip. heating control is in place.

However, with such a method, it is extremely difficult to quickly and accurately control the large number of burners provided in the oxidation furnace, and adjustments tend to be delayed, and variations in operation due to individual differences among workers are unavoidable. However, if the control is accurate, it cannot be expected, and uneven baking will occur. Uneven firing leads to shrinkage of the copper strip and peeling of the galvanized layer, so it must be avoided as much as possible. In addition, this method only changes the amount of fuel supplied to the burner, not the amount of air supplied.
It is impossible to maintain an optimal air-fuel ratio, and there are also problems in terms of thermal efficiency.

Adjusting the air supply amount according to the fuel amount in order to maintain the optimum air-fuel ratio would require extremely complicated operations, making it virtually impossible to adjust the air supply amount. The invention is a direct-fired heating furnace that can quickly and accurately adjust the burner combustion according to the firing state of the copper strip to eliminate uneven firing as much as possible, and that can always maintain the optimal air-fuel ratio of the burner. The object of the present invention is to provide a method for heating a copper strip.

In the present invention, when a steel strip is continuously heated by passing through a direct-fired heating furnace having a plurality of burners on the ceiling, the burners are divided into a front-stage burner group and a rear-stage burner group, and the latter burner group is further heated. It is divided into a plurality of blocks that are arranged in parallel in a direction perpendicular to the direction in which the copper strip travels, and a branch pipe is arranged from the air main pipe and the fuel gas main pipe for each of the former stage block and the latter stage blocks, and connected to each burner. A differential pressure regulating valve mechanism is provided in a branch pipe from the fuel gas main pipe or a branch pipe from the air main pipe, and the differential pressure regulating valve mechanism and the air pressure regulating valve provided in the air branch pipe or the fuel gas branch pipe are connected to the differential pressure regulating valve mechanism. The fuel gas pressure or air pressure is automatically changed according to the air pressure or fuel gas pressure by connecting the downstream side of the provided fuel gas pressure control valve with a pipe so that the optimum air-fuel ratio is always maintained immediately after passing through the heating furnace. The temperature of the copper strip is detected for each part corresponding to each block in the latter stage, and based on the detected value, the air pressure or The gist of this paper is a method for heating a copper strip in a direct-fired heating furnace, which is characterized by controlling the fuel gas pressure and bringing the temperature of the copper strip in each subsequent block to a target temperature. In other words, the method of the present invention raises the temperature of the copper strip to a target temperature while maintaining the air-fuel ratio of all burners in the front and rear stages to an optimum level, detects the temperature distribution in the width direction of the copper strip immediately after passing through the heating furnace, and measures the temperature distribution of the copper strip in the width direction. Depending on the detected value,
The air pressure or fuel gas pressure to the burner is finely adjusted for each of the multiple parallel blocks in the latter stage to manage the firing state of the steel strip while maintaining the optimum air-fuel ratio, enabling quick and accurate heating control. As a result, it is possible to effectively eliminate uneven firing, and the optimum air-fuel ratio is always ensured for all burners, so it has the characteristics of being highly effective in saving fuel.0 The present invention is as follows: will be explained in more detail with reference to the drawings.

FIG. 1 is a schematic diagram showing the state of burner installation in a direct-fired heating furnace, with (a) showing a plan view and (b) showing a longitudinal sectional front view. In this type of heating furnace, the burners generally have the sign (la
) are installed in high density on the ceiling (2) of the furnace, and a few are installed on both side walls (3) (3) as shown in (1b).

In carrying out the method of the present invention, first, the above-mentioned ceiling burner (1
) group is divided into a plurality of blocks, for example, as shown by broken lines in FIG. In other words, the ceiling burner group is first placed in the front stage (2).
Separate into the following part■. It is preferable to divide the first stage (2) so that it accounts for the largest number of ceiling burners among the total number of ceiling burners.

Next, the meeting group in the second stage (2) is further divided into a plurality of blocks (BI XB2) arranged in parallel in the direction perpendicular to the line. Although the number of these divisions approaches three in the illustrated example, this is not particularly limited. However, depending on the actual L1 steel strip width, it is undeniable that the control effect is not good if there are only two divisions, while if there are more than four divisions, the device will only become more complicated, but there will be no significant difference in effectiveness; It seems appropriate to divide it into four categories. In addition, regarding the side wall burner (1b), it is considered as one block (Q,
It is best to incorporate it into the control as described below.

The burners of the heating furnace are thus divided into sections, and the fuel and air supply systems to the burners are constructed as follows.

That is, FIG. 2 shows the supply system described in item 1 suitable for carrying out the method of the present invention. 6) and from there each of the blocks (A) (
Branch pipe (71X72) leading to BIXB2XB3XQ
..., and each block is branched and supplied to each burner from the same branch pipe (7). The main pipe (6) is provided with an air main pressure regulating valve (8), and each branch pipe (71X) branched from there.
7. Air pressure control valve for each block (91X92)
...is installed. On the other hand, regarding the fuel supply system,
The fuel gas from nine coke ovens (not shown) is sent to the main pipe OQ, and from there it is divided into branch pipes (111), (112), etc. provided corresponding to each block as described above, and is distributed to each block. from the same branch pipe 0]) to each burner (
It's happening. The main pipe (10) is provided with a source pressure control valve (6), and each of the branch pipes (IIIXII...) is equipped with block-specific differential pressure control valves (13x132). The control valve 03 is a so-called ratio regulator that automatically adjusts the fuel gas pressure to a preset air-fuel ratio by reflecting the air pressure changes made by the corresponding air pressure control valves (91), (92), etc. It is used.

It should be noted that such a differential pressure regulating valve mechanism does not necessarily have to be adjusted based on the air pressure side, but may be provided so as to be operated from the fuel gas pressure side.

Now, the heating method based on the present invention will be explained step by step.■ The temperature of the copper strip (baked state) immediately after it comes out of the heating furnace is measured at the portion corresponding to each of the subsequent blocks (& ) (B2)... For example, the center position (P
l) (B2)... Thermometer (4rX4s)...
・Continuous detection.

(2) Based on this detected value, the air source pressure regulating valve (8) is first adjusted in order to bring the average heating temperature of the copper strip closer to the target value. That is, for example, calculate the average value of the heating temperatures detected above, consider this value as the actual measurement value, compare it with the target copper strip heating temperature, calculate the difference between them, and determine the air source based on the positive or negative value of this difference. The pressure regulating valve (8) is adjusted to either increase or decrease the flow rate. Now, if the value obtained by subtracting the actual measured value from the target value is positive, then the source pressure regulating valve (8
) may be adjusted in the direction of increasing the flow rate. This operation increases the overall optimum air-fuel ratio to maintain it, thereby intensifying the burner combustion of all blocks and increasing the heating temperature of the copper strip overall, i.e. the copper strip average heating temperature is the target. [
;It will get closer.

■ In addition to the above operations, only for the burner group in the latter stage ■, based on each of the detected values of the thermometer (41
・Pneumatic pressure control valve for each block of branch pipe connected to (9!)
(9F) An operation is performed to make the heating temperature of the steel strip uniform in the width direction by adjusting... For example, in synthesis,
If the actual value measured by the thermometer (4) is lower than the target value, the air pressure control valve (φ) that controls the air supply amount to the block (B) corresponding to this measurement point is adjusted in the direction of increasing the flow rate. When the air pressure to the block (B10 increases), the air pressure fluctuation is transmitted to the differential pressure regulating valve by the pipe connecting the downstream of the air pressure regulating valve and the differential pressure regulating valve.As a result, the fuel supply amount is increased by the action of the differential pressure regulating valve 03. The air-fuel ratio also increases with the optimum air-fuel ratio, intensifying the combustion of the burner in block (B1), increasing the heating temperature of the copper strip at the measurement location, and reducing the difference from the target temperature. For each block,
By performing such control, the heating temperature of the copper strip tends to be uniform in the middle direction.

``By repeating and continuously performing the operations in ■ and ■ above during operation, uneven burning can be prevented as much as possible, the desired baked soil condition can be continuously obtained, and fuel consumption can also be reduced. Minimized.

It is most preferable to perform the following operations completely automatically by incorporating a thermal control device, but it is most preferable to use a thermometer (4).
A device (5) is installed that has the function of clearly displaying the actual measured values and the average value, and the function of operating each control valve, and the operator remotely controls the control valve from the operator's cab while monitoring the displayed values. Even if a semi-automatic method is used, high precision heating can be expected.

The present inventors installed a copper strip (size: Q, 35 mm thick x 914 mm width) in an oxidizing furnace of a continuous hot-dip galvanizing line at a line speed of 90°C so that the temperature was 37°C at the outlet of the oxidizing furnace.
m/'I-CI3.4 T/H), heating control was carried out based on the method described above, but as a result,
Previously, the fuel consumption rate was 28ONm'/H, but it has been reduced to the same <24ONm. It is also possible to minimize the occurrence of peeling of the plating layer by implementing the method of the present invention.
The inventors have already confirmed this. Therefore, the present invention is effective in reducing fuel consumption and preventing uneven heating during heating of steel strips in direct-fired heating furnaces, and is particularly applicable to oxidation furnace control in galvanizing lines to improve the quality of galvanized steel sheets. It can be said that it is extremely effective.

[Brief explanation of the drawing]

Figure 1 shows an example of burner arrangement for a direct-fired heating furnace.
(A) is a plan view, (B) is a longitudinal sectional front view, and FIG. 2 is an explanatory diagram for explaining heating control based on the method of the present invention. In the figure 1a: ceiling burner, 1b: side wall bar, -su, 2:
Ceiling, 3: Side wall, 4: Thermometer, 5: Temperature display device, 6:
Air main pipe, 7: Air branch pipe by block, 8: Air main pressure control valve, 9 Air pressure control valve by Niblock, 10: Fuel gas main pipe, 11 Fuel gas branch pipe by Niblock, 12: Fuel gas main pressure Control valve, differential pressure control valve for 13 nib blocks. Figure 1 (a) (b) Figure 2 ζ

Claims (1)

[Claims] (1) When continuously heating a steel strip by passing it through a direct-fired heating furnace that has multiple burners on the ceiling, the burners are divided into a front-stage burner group and a rear-stage burner group, and the latter burner group is further heated using copper. It is divided into a plurality of blocks parallel to each other in a direction perpendicular to the direction of belt movement, and a branch pipe is provided from the air main pipe and the fuel gas main pipe for each of the front stage block and the rear stage blocks and connected to each burner. However, a differential pressure regulating valve mechanism is provided in the branch pipe from the fuel gas main pipe and the branch pipe from the air main pipe, and the differential pressure regulating valve mechanism and the air pressure regulating valve provided in the air branch pipe or the fuel gas branch pipe The fuel gas pressure or air pressure is automatically changed according to the air pressure or fuel gas pressure by connecting it to the downstream side of the fuel gas pressure control valve installed in the heating furnace, so that the optimum air-air ratio is always maintained. The temperature of the copper strip immediately after passing through is detected for each part corresponding to each block in the latter stage, and based on the detected value, the air pressure is adjusted by the air pressure control valve of each air branch pipe or the fuel gas pressure control valve of the fuel gas branch pipe. A method for heating a copper strip in a direct-fired heating furnace, characterized by controlling the pressure or fuel gas pressure and bringing the temperature of the copper strip in each subsequent block to a target temperature.